Regenerable solvent mixtures for acid-gas separation

ABSTRACT

A solvent system comprising a diluent and a nitrogenous base for the removal of CO2 from mixed gas streams is provided. Also provided is a process for removing CO2 from mixed gas streams using the disclosed solvent system. The solvent system may be utilized within a gas processing system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. application Ser. No.13/820,027 filed Feb. 28, 2013, which is a U.S. National Phase ofPCT/US2011/050452, filed Sep. 3, 2011, which claims priority to U.S.Provisional Patent Application 61/379,827, filed Sep. 3, 2010. All ofthese applications are incorporated by reference herein in theirentireties.

FIELD OF THE INVENTION

The present invention relates to solvent systems for the removal ofspecific components of gas streams, as well as devices and methods usingsuch systems. More specifically, the invention can provide for removalof acid gases, such as CO₂, SO₂, COS, CS₂ and NOx. The invention furthercan provide for continuous operation of devices and methods using thesystem. Further, the inventive methods can utilize multipleabsorption/desorption means, including gas absorption/desorption and/orphase-enhanced absorption/desorption.

BACKGROUND OF THE INVENTION

Various strategies are being pursued to minimize the production and/orrelease of undesirable emissions from combustion processes. One suchstrategy is the development of technologies for the specific removal ofacid gases from gas mixtures, such as the exhausts of carbon combustionprocesses. The separation of acid gases, such as CO₂, from gas mixtureshas been carried out industrially for over a hundred years, although noknown process has been used on a large scale such as that required bylarge, industrial power plants. Of the numerous processes used for CO₂separation, current technology mainly focuses on the use of varioussolvents, such as alkali carbonates in the BENFIELD™ Process (UOP, LLC),alcoholamines in the ECONAMINE FG PLUS™ process (Fluor Corporation), andalcohols, diols, and ethers in the RECTISOL® process (Lurgi, GMBH) andthe SELEXOL™ solvent (The Dow Chemical Company). In a typicalsolvent-based process, the gas mixture to be treated is passed through aliquid solvent that interacts with acidic compounds in the gas stream(e.g., CO₂ and SO₂) and separates them from non-acidic components. Theliquid becomes rich in the acid-gas components, which are then removedunder a different set of operating conditions so that the solvent can berecycled for additional acid-gas removal.

Methods for removal of the acid-gas components from rich solventsinvolve pressure and temperature change. Depending on the temperature ofthe gas mixture and the partial pressure of the acid-gas in the mixture,certain solvents are preferred for specific applications. When a solventoperates to interact with an acid-gas by chemical absorption, anexothermic chemical reaction occurs. The reversal of this reactionrequires at least the amount of energy to be added back to the richsolvent that was produced by the forward reaction, not to mention theenergy needed to bring the rich solvent to the temperature wherereversal is appreciable and to maintain conditions to complete thereverse reaction to an appreciable extent. The energy required to obtainpurified acid-gas from the rich solvent contributes to the cost of thepurified product. In particular, the cost of the purified acid-gas hasbecome a significant hurdle for the application of solvent technologiesto fossil-fuel fired power plants for the removal of acid gases fromflue gas.

Non-aqueous solvents have been used to remove CO₂ from natural gasstreams and require less energy for regeneration. Single-componentalcoholic physisorption solvents such as RECTISOL™ and SELEXOL® arecommercially available for CO₂ separation but perform poorly in thehumid, near-ambient pressure conditions associated with flue gas.Alcoholamines and amines have been combined with alcohols, diols, andcyclic carbonates by various researches to form “hybrid solvents” whosereaction mechanisms and kinetics have been studied in the literature.See, Alvarez-Fuster, et al., Chem. Eng. Sci. 1981, 36, 1513; Ali, etal., Separation and Purification Technology 2000, 18, 163; Usubharatana,et al., Energy Procedia 2009, 1, 95; and Park, et al., Sep. Sci.Technol. 2005, 40, 1885. In addition, a process known as the“phase-transitional absorption method” has been disclosed in relation tomethods for deacidizing gaseous mixtures, which generally consists ofthe absorption of acid gases into an “absorbing phase” of less densitythan water consisting of a nitrogenous base and an alcohol, followed bytransfer of the absorbed acid gas into an aqueous “carrier phase”. Theaqueous carrier phase can be regenerated in a regenerator. The processclaims to save energy by absorbing an acid gas at a faster rate than inan absorbing phase alone, and by avoiding the energy required to pump arich absorbing phase to a separate regenerator by utilizing gravity totransfer the acid gas between phases in a single column for absorptionand regeneration.

Ionic liquids are another non-aqueous solvent currently being developed.These solutions consist completely of ion pairs which are in the liquidstate near room temperature. They have low regeneration requirements buthave not surpassed aqueous amine solvents in performance due to factorsincluding CO₂ loading capacity, viscosity, cost, and, importantly,degradation by water. Using a non-aqueous liquid solvent to separate CO₂from gas mixtures containing water vapor can lead to the accumulation ofH₂O in the liquid solution either as a single-phase or bi-phasesolution, depending upon the process conditions (e.g., pressure,temperature, H₂O concentration) and the affinity of the non-aqueoussolvent for H₂O. H₂O accumulation is detrimental to the CO₂ separationand purification process, since more energy will be required for solventregeneration due to the necessity of continually removing water from thesolvent.

Another group of non-aqueous liquids which could be developed to addressmany of the problems affecting CO₂ solvents are room temperatureswitchable ionic liquids. These equimolar mixtures of amidine orguanidine nitrogen bases and alcohols are non-ionic room temperatureliquids that react with CO₂ to form room-temperature ionic liquids.Typically, the conductivity of equimolar mixtures increases by one ortwo orders of magnitude when CO₂ is added. Importantly, these solventshave higher CO₂ loadings than some aqueous amines, and are regenerableunder milder conditions. While these solvents are a promisingalternative technology, those that have been previously disclosed arepoorly suited for flue gas applications due to their chemistries withrespect to water, which typically is a major component of flue gas. CO₂is captured via the formation of amidinium and guanidinium alkylcarbonate salts derived from the conjugate bases of the deprotonatedalcohol components. However, if the conjugate base of the alcohol is aweaker acid than water, an acid-base equilibrium is established betweenthe alcohol-conjugate base and water, which favors deprotonation ofwater and reformation of the protonated alcohol. The conjugate base ofwater, the hydroxide ion, reacts favorably with CO₂ to form abicarbonate anion, which requires more energy to reverse than alkylcarbonate anions.

Accordingly, it would be beneficial to formulate a new solvent systemcapable of effectively removing acid gases from gas streams(particularly water-containing gas streams) and which can be regeneratedat a lower temperature and energy load than the solvents currentlyutilized for such purposes.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a solvent system for theremoval of acidic gases, such as CO₂, from a gas stream. In someembodiments, the solvent system comprises a nitrogenous base and one ormore diluents. In some embodiments, a solvent system according to theinvention can comprise a nitrogenous base and an acidic component thatacts as a diluent.

In one embodiment, the invention provides a solvent system comprising asolution formed of: a nitrogenous base having a hydrogen atom leavinggroup (preferably having a nitrogen with a hydrogen atom leaving group);and a diluent, wherein the nitrogenous base has a structure such that itreacts with an acidic gas so as to form a carbamate salt or a heteroatomanalogue of a carbamate salt without any substantial formation of acarbonate ester or a heteroatom analogue of a carbonate ester.

The nitrogenous base and the diluent can vary. For example, in someembodiments, the diluent is selected from the group consisting offluorinated alcohols, optionally substituted phenols, nitrogenheterocycles, and mixtures thereof. In some embodiments, the diluent isspecifically selected from the group consisting of:2,2,3,3,4,4,5,5-octafluoropentanol (“OFP”); 2,2,3,3-tetrafluoropropanol(“TFP”); 2,2,3,3,3-pentafluoropropanol (“PFP”);2,2,3,3,4,4-hexafluorobutanol (“HFB”); 2,2,2-trifluoroethanol (“TFE”);nonafluoro-1-hexanol; 4,4,5,5,6,6,7,7,7-nonafluoroheptanol;1,1,3,3-hexafluoro-2-phenyl-2-propanol; 4-methoxyphenol (“4-MeOPh”);4-ethoxyphenol (“4-EtOPh”); 2-ethoxyphenol; 4-propoxyphenol; imidazole;benzimidazole; N-methyl imidazole; 1-trifluoroacetylimidazole;1,2,3-triazole; 1,2,4-triazole; 2-trifluoromethylpyrazole;3,5-bistrifluoromethylpyrazole; 3-trifluoromethylpyrazole; and mixturesthereof. In certain embodiments, the diluent is selected from the groupconsisting of alcohols, ketones, aliphatic hydrocarbons, aromatichydrocarbons, nitrogen heterocycles, oxygen heterocycles, aliphaticethers, cyclic ethers, esters, and amides and mixtures thereof. In someembodiments, the diluent may be selected from the group consisting offluorinated alcohols, fluorinated ketones, fluorinated aliphatichydrocarbons, fluorinated aromatic hydrocarbons, fluorinated nitrogenheterocycles, fluorinated oxygen heterocycles, fluorinated aliphaticethers, fluorinated cyclic ethers, fluorinated esters, and fluorinatedamides and mixtures thereof. In certain specific embodiments, thediluent is selected from the group consisting of toluene, p-xylene,1-methylnaphthalene, 2,4,6-dimethylaminophenol, benzylalcohol,2,6-dimethylcyclohexanone, 3,5-lutidine, cyclohexanone, aniline,pyridine, 2-fluoroacetylphenone, 1-fluorodecane,2,4-difluorobenzophenone, 2-fluoro-3-trifluoromethylaniline,2-fluoroaniline, 4-fluoroaniline, 3-trifluoromethylacetophenone,2-trifluoromethylacetophenone,bis(2,2,2-trifluoroethyl)methylphosphonate,4-fluoro-3-(trifluoromethyl)benzaldehyde and mixtures thereof.

In some embodiments, the the nitrogenous base has a pKa of about 8 toabout 15. In some embodiments, the nitrogenous base is selected from thegroup consisting of primary amines, secondary amines, diamines,triamines, tetraamines, pentamines, cyclic amines, cyclic diamines,amine oligomers, polyamines, alcoholamines, guanidines, amidines, andmixtures thereof. Certain specific nitrogenous bases include, but arenot limited to, 1,4-diazabicyclo-undec-7-ene (“DBU”);1,4-diazabicyclo-2,2,2-octane; piperazine (“PZ”); triethylamine (“TEA”);1,1,3,3-tetramethylguanidine (“TMG”); 1,8-diazabicycloundec-7-ene;monoethanolamine (“MEA”); diethylamine (“DEA”); ethylenediamine (“EDA”);1,3-diamino propane; 1,4-diaminobutane; hexamethylenediamine;1,7-diaminoheptane; diethanolamine; diisopropylamine (“DIPA”);4-aminopyridine; pentylamine; hexylamine; heptylamine; octylamine;nonylamine; decylamine; tert-octylamine; dioctylamine; dihexylamine;2-ethyl-1-hexylamine; 2-fluorophenethylamine; 3-fluorophenethylamine;3,5-difluorobenzylamine; 3-fluoro-N-methylbenzylamine;4-fluoro-N-methylbenzylamine; imidazole; benzimidazole; N-methylimidazole; 1-trifluoroacetylimidazole; 1,2,3-triazole; 1,2,4-triazole;and mixtures thereof.

In some embodiments, the solvent system is immiscible with water. Forexample, in certain embodiments, the solvent system has a solubilitywith water of less than about 10 g of solvent per 100 mL of water.

In another aspect of the invention is provided a process for the removalof acid gas from a gas stream, comprising contacting an acidgas-containing gas stream with a solvent system comprising a liquidcomprising: a nitrogenous base having a hydrogen atom leaving group; anda diluent, wherein the nitrogenous base has a structure such that itreacts with an acidic gas so as to form a carbamate salt or a heteroatomanalogue of a carbamate salt without any substantial formation of acarbonate ester or heteroatom analogue of a carbonate ester.

In some embodiments, the process further comprises outputting an acidgas-rich solvent and an acid gas-lean gas stream. In some embodiments,the process further comprises regenerating the acid gas-rich solvent byapplying heat to form a regenerated solvent comprising a lower contentof acid gas than present in the acid gas-rich solvent. The heat appliedby the regeneration component may be, for example, derived from a sourceselected from the group consisting of low-pressure steam, hot flue gas,or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scheme showing a reaction pathway employed for capturing CO₂using solvent mixtures comprising an acid component and a nitrogenousbase;

FIG. 2 is a diagram of a reboiler-based system embodied by the presentinvention for the capture and regeneration of acidic gases from a mixedgas stream;

FIG. 3 is a diagram of a reboiler-free system embodied by the presentinvention for the capture of acidic gases from a mixed gas stream;

FIG. 4 is a diagram of a reboiler-assisted system embodied by thepresent invention for the capture of acidic gases from a mixed gasstream;

FIG. 5 is a diagram of a waste heat reboiler system embodied by thepresent invention for the capture of acidic gases from a mixed gasstream;

FIG. 6 is a diagram of a waste heat utilization system embodied by thepresent invention for the capture of acidic gases from a mixed gasstream;

FIG. 7 is a fluorine NMR spectrum of 2-fluorophenethylamine and2,2,3,3,4,4,5,5-octafluoropentanol before (top) and after (bottom)reaction with CO₂, showing six unique resonances in the product;

FIG. 8 is fluorine NMR spectra of 2-FPEA before (top) and after (bottom)reaction with CO₂;

FIG. 9 is a ¹H NMR spectrum showing transformation of2-fluorophenethylamine into 2-fluorophenethylamine carbamate uponreaction with carbon dioxide;

FIG. 10 shows reaction pathways with carbon dioxide for the solvent3-fluoro-N-methylbenzylamine in 4,4,5,5,6,6,7,7,7-nonafluorheptanol,where all relevant hydrogen and fluorine nuclei are labeled fordiscussion herein;

FIG. 11 is fluorine NMR spectra following the transformation of3-FNMBA/NFHp solvent (top) with the addition of CO₂ (bottom);

FIG. 12 is ¹H NMR spectra of the transformation occurring with purgingof 3-FNMBA/NFHp with CO₂, showing fluorinated alcohol ¹H resonancesunaffected by CO₂ absorption;

FIG. 13 is fluorine NMR spectra of 3-FNMBA before (top) and after(bottom) reaction with CO₂; and

FIG. 14 is ¹H NMR spectra showing transformation of3-fluoro-N-methylbenzylamine into 3-fluoro-N-methylbenzylamine carbamateupon reaction with carbon dioxide.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements. As used in thisspecification and the claims, the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.

In one aspect of the present invention is provided a liquid solventsystem. The solvent system may be used for the separation of acidicgases from gas mixtures. The term “acid gas” is intended to refer to anygas component that can result in formation of an acid when mixed withwater. Non-limiting examples of acid gases encompassed by the presentinvention include CO₂, SO₂, COS, CS₂ and NOx. For simplicity, theinvention is described below in relation specifically to CO₂. It isunderstood, however, that the present invention encompasses methods andsystems for removal of any acid gas component from a gas stream.

In certain embodiments, the solvent system is regenerable in that theacidic gases can be released from the solvent, and the solvent can bereused to separate additional acidic gases from further gas mixtures. Inparticular embodiments, the solvent system is regenerable attemperatures lower than those typically required for solvents used forsuch purposes.

In some embodiments, the solvent system of the present inventioncomprises a mixture of a nitrogenous base component with a non-aqueousdiluent. The non-aqueous diluent can be, but is not necessarily, arelatively acidic component. The term “relatively acidic component” asused herein is interchangeable with the term “acidic component” and isunderstood to mean a material having an acidity that is greater than theacidity of water, preferably substantially greater than the acidity ofwater. For example, in some embodiments, the diluent can have a pKa ofless than about 15, less than about 14, less than about 13, less thanabout 12, less than about 11, or less than about 10. In someembodiments, the diluent has a pKa of the alcohol component is about 6to about 15, about 7 to about 15, about 8 to about 15, about 9 to about15, about 6 to about 14, about 7 to about 14, about 8 to about 13, about9 to about 13, about 6 to about 12, about 7 to about 12, about 8 toabout 12, about 9 to about 12, about 6 to about 11, about 7 to about 11,about 8 to about 11, about 9 to about 11, about 6 to about 10, about 7to about 10, or about 8 to about 10.

Exemplary classes of diluents (e.g., relatively acidic diluents) thatmay be used according to the invention include, but are not limited tothe following: fluorinated alcohols; optionally substituted phenols; andnitrogen heterocycles. Fluorinated alcohols useful according to theinvention may comprise any compound having the formula R—OH, where R isan alkyl group (e.g., C₁-C₁₀ alkyl, C₁-C₈ alkyl, C₁-C₆ alkyl, C₂-C₁₀alkyl, C₂-C₈ alkyl, C₂-C₆ alkyl, C₃-C₁₀ alkyl, C₃-C₈ alkyl, or C₃-C₆alkyl) and wherein one or more hydrogen atoms of the alkyl group issubstituted with fluorine. In some embodiments, the number of hydrogenatoms replaced with fluorine can be two, three, four, five, six, seven,eight, nine, or even more as may be deemed useful. In furtherembodiments, one or more of the hydrogen atoms of the alkyl group mayoptionally be replaced with one or more other substituents, including,but not limited to, C₁-C₆ alkyl, C₁-C₆ alkoxy, and halo substituents.Optionally substituted phenols useful in the invention are understood tomean phenols wherein one or more of the hydrogen atoms on the phenylring may be replaced with a substituent. Non-limiting, exemplaryreplacement groups for one or more of the hydrogen atoms on the phenylring include C₁-C₆ alkyl, C₁-C₆ alkoxy, and halo. Nitrogen heterocyclesare understood to mean any cyclic compound including at least onenitrogen atom in the ring structure (including but not limited toimidazoles, pyrazoles, and triazoles) and being optionally substitutedsuch that one or more of the hydrogen atoms on the ring structure may bereplaced with a substituent. Non-limiting, exemplary replacement groupsfor one or more of the hydrogen atoms on the ring include C₁-C₆ alkyl,C₁-C₆ alkoxy, and halo.

In some specific embodiments, the diluent (e.g., relatively acidicdiluents) may be selected from the group consisting of:2,2,3,3,4,4,5,5-octafluoropentanol (“OFP”); 2,2,3,3-tetrafluoropropanol(“TFP”); 2,2,3,3,3-pentafluoropropanol (“PFP”);2,2,3,3,4,4-hexafluorobutanol (“HFB”); 2,2,2-trifluoroethanol (“TFE”);nonafluoro-1-hexanol; 4,4,5,5,6,6,7,7,7-nonafluoroheptanol;1,1,3,3-hexafluoro-2-phenyl-2-propanol 4-methoxyphenol (“4-MeOPh”);4-ethoxyphenol (“4-EtOPh”); 2-ethoxyphenol; 4-propoxyphenol; imidazole;benzimidazole; N-methyl imidazole; 1-trifluoroacetylimidazole;1,2,3-triazole; 1,2,4-triazole; 2-trifluoromethylpyrazole;3,5-bistrifluoromethylpyrazole; 3-trifluoromethylpyrazole; and mixturesthereof.

In other embodiments, the non-aqueous diluent is not a relatively acidiccomponent, and does not have a pKa that falls within the ranges notedabove. For example, the non-aqueous diluent may, in certain embodiments,have a pKa greater than about 15.

In certain embodiments, the non-aqueous diluent used in the solventsystem may be generally selected from the group consisting of alcohols,ketones, aliphatic hydrocarbons, aromatic hydrocarbons, nitrogenheterocycles, oxygen heterocycles, aliphatic ethers, cyclic ethers,esters, and amides and mixtures thereof. In more specific embodiments,the diluent may be selected from the group consisting of fluorinatedalcohols, fluorinated ketones, fluorinated aliphatic hydrocarbons,fluorinated aromatic hydrocarbons, fluorinated nitrogen heterocycles,fluorinated oxygen heterocycles, fluorinated aliphatic ethers,fluorinated cyclic ethers, fluorinated esters, and fluorinated amidesand mixtures thereof. In specific embodiments the diluent may beselected from the group consisting of toluene, p-xylene,1-methylnaphthalene, 2,4,6-dimethylaminophenol, benzylalcohol,2,6-dimethylcyclohexanone, 3,5-lutidine, cyclohexanone, aniline,pyridine, 2-fluoroacetylphenone, 1-fluorodecane,2,4-difluorobenzophenone, 2-fluoro-3-trifluoromethylaniline,2-fluoroaniline, 4-fluoroaniline, 3-trifluoromethylacetophenone,2-trifluoromethylacetophenone, bis(2,2,2-trifluoroethyl)methylphosphonate, 4-fluoro-3-(trifluoromethyl)benzaldehyde and mixtures thereof.Further, diluents within this list can be combined with diluents notedto be “relatively acidic diluents” as listed above.

The nitrogenous base according to the present invention can becharacterized as any nitrogenous base having a proton that can bedonated from a nitrogen, which reacts with an acid gas via a carbamatepathway and avoids reaction with the acid gas to form carbonate esters.The nitrogenous base component may, in certain embodiments, be almostany nitrogenous base that meets this requirement including, but notlimited to, primary amines, secondary amines, diamines, triamines,tetraamines, pentamines, cyclic amines, cyclic diamines, amineoligomers, polyamines, alcoholamines, guanidines, amidines, and thelike. In some embodiments, the nitrogenous base can have a pKa of about8 to about 15, about 8 to about 14, about 8 to about 13, about 8 toabout 12, about 8 to about 11, or about 8 to about 10. In certainembodiments, the nitrogenous base component has a pKa less than about11.

A primary amine is understood to be a compound of the formula NH₂R,where R can be a carbon-containing group, including but not limited toC₁-C₂₀ alkyl. A secondary amine is understood to be a compound of theformula NHR₁R₂, wherein R₁ and R₂ are independently carbon-containinggroups, including but not limited to C₁-C₂₀ alkyl, wherein R, R₁, and R₂are independently carbon-containing groups, including but not limited toC₁-C₂₀ alkyl. One or more of the hydrogens on R, R₁, and R₂ mayoptionally be replaced with one or more substituents. For example, oneor more of the hydrogens on R, R₁, or R₂ may be replaced with optionallysubstituted C₁-C₆ alkyl, optionally substituted C₁-C₆ alkoxy, optionallysubstituted C₂-C₁₀ alkenyl; optionally substituted C₂-C₁₀ alkynyl;optionally substituted alkaryl; optionally substituted arylalkyl;optionally substituted aryloxy; optionally substituted heteroaryl;optionally substituted heterocycle; halo (e.g., Cl, F, Br, and I);hydroxyl; halogenated alkyl (e.g., CF₃, 2-Br-ethyl, CH₂F, CH₂CF₃, andCF₂CF₃); optionally substituted amino; optionally substitutedalkylamino; optionally substituted arylamino; optionally substitutedacyl; CN; NO₂; N₃; CH₂OH; CONH₂; C₁-C₃ alkylthio; sulfate; sulfonicacid; sulfonate esters (e.g., methanesulfonyl); phosphonic acid;phosphate; phosphonate; mono-, di-, or triphosphate esters; trityl ormonomethoxytrityl; CF₃S; CF₃SO₂; or silyl (e.g., trimethylsilyl,dimethyl-t-butylsilyl, and diphenylmethylsilyl). Cyclic amines areamines wherein the nitrogen atom forms part of the ring structure, andmay include, but are not limited to, aziridines, azetidines,pyrrolidines, piperidines, piperazines, pyridines, pyrimidines,amidines, pyrazoles, and imidazoles. Cyclic amines may comprise one ormore rings and may optionally be substituted with one or moresubstituents as listed above. In some embodiments, the nitrogenous basehas a guanidine structure, which is optionally substituted with one ormore substituents as noted above. In some embodiments, the nitrogenousbase has an amidine structure, which is optionally substituted with oneor more substituents as noted above. In some embodiments, thenitrogenous base may be a diamine. In some embodiments, the nitrogenousbase may be a primary or secondary alcoholamine. Alcoholamines are alsoknown as amino alcohols and contain both an alcohol and amine group. Theamine group of the alcoholamine may be any type of amine as disclosedherein. In some embodiments, the alcoholamine is a primary, secondary,or tertiary alcohol amine.

In certain embodiments, the primary or secondary amine may be selectedfrom amines functionalized with fluorine-containing-alkyl-aromaticgroups. In specific embodiments, the amine may be selected from thegroup consisting of 2-fluorophenethylamine, 3-fluorophenethylamine,4-fluorophenethylamine, 2-fluoro-N-methylbenzylamine,3-fluoro-N-methylbenzylamine, and 4-fluoro-N-methylbenzylamine,3,5-di-fluorobenzylamine, D-4-fluoro-alpha-methylbenzylamine, andL-4-fluoro-alpha-methylbenzylamine.

In certain embodiments, the nitrogenous base may be selected from thegroup consisting of 1,4-diazabicyclo-undec-7-ene (“DBU”);1,4-diazabicyclo-2,2,2-octane; piperazine (“PZ”); triethylamine (“TEA”);1,1,3,3-tetramethylguanidine (“TMG”); 1,8-diazabicycloundec-7-ene;monoethanolamine (“MEA”); diethylamine (“DEA”); ethylenediamine (“EDA”);1,3-diamino propane; 1,4-diaminobutane; hexamethylenediamine;1,7-diaminoheptane; diethanolamine; diisopropylamine (“DIPA”);4-aminopyridine; pentylamine; hexylamine; heptylamine; octylamine;nonylamine; decylamine; tert-octylamine; dioctylamine; dihexylamine;2-ethyl-1-hexylamine; 2-fluorophenethylamine; 3-fluorophenethylamine;3,5-difluorobenzylamine; 3-fluoro-N-methylbenzylamine;4-fluoro-N-methylbenzylamine; imidazole; benzimidazole; N-methylimidazole; 1-trifluoroacetylimidazole; 1,2,3-triazole; 1,2,4-triazole;and mixtures thereof. In certain embodiments, the nitrogenous base maybe a guanidine or amidine.

In some embodiments, the solvent system may include a mixture comprisinga nitrogenous base and a diluent, which components may be present inroughly equal proportions by molarity (i.e. are present in equimolaramounts). In certain embodiments, the diluent is present in excess. Incertain embodiments, the nitrogenous base is present in excess. Forexample, the molar ratio of nitrogenous base to diluent can be about 1:1to about 100:1, for example, about 1.1:1 to about 20:1, 1.1:1 to about15:1, 1.1:1 to about 10:1, 1.1:1 to about 5:1, 1.1:1 to about 3:1, about2:1 to about 20:1, about 2:1 to about 15:1, 2:1 to about 10:1, 2:1 toabout 5:1, about 3:1 to about 20:1, about 3:1 to about 15:1, about 3:1to about 10:1, about 4:1 to about 20:1, about 4:1 to about 15:1, about4:1 to about 10:1, about 5:1 to about 20:1, about 5:1 to about 15:1, orabout 5:1 to about 10:1. Although not wishing to be bound by theory, itis believed that the use of an additional component can be useful toreduce or prevent precipitation of solids in the solvent system. In someembodiments, the solvent system may further comprise one or moreadditional components. The additional components may be added, forexample, to increase the solubility of the captured CO₂ product in thesolvent system, and thus avoid the formation of precipitates. In otherembodiments, however, solids formation may be desirable, and suchformation may be enhanced by altering the concentration of one or moresolvent components.

In some embodiments, the solvent system of the present invention isparticularly useful for capturing CO₂ from a gas stream. The gas streammay be a mixed gas stream, having one or more other components inaddition to CO₂. When a solution comprising a solvent system of thepresent invention is purged with a gas mixture containing CO₂, thecomponents of the solvent system undergo a chemical reaction with CO₂,binding the CO₂ in the solution. In some embodiments, the solventsystems of the present invention have high CO₂ loadings. For example,the solvent systems may be useful for capturing or removing greater thanabout 0.05 moles CO₂ per mole of nitrogenous base, greater than about0.1 moles CO₂ per mole of nitrogenous base, greater than about 0.2 molesCO₂ per mole of nitrogenous base, greater than about 0.3 moles CO₂ permole of nitrogenous base, greater than about 0.4 moles CO₂ per mole ofnitrogenous base, greater than about 0.5 moles CO₂ per mole ofnitrogenous base, greater than about 0.6 moles CO₂ per mole ofnitrogenous base, greater than about 0.7 moles CO₂ per mole ofnitrogenous base, greater than about 0.8 moles CO₂ per mole ofnitrogenous base, greater than about 0.9 moles CO₂ per mole ofnitrogenous base, or greater than about 1 mole CO₂ per mole ofnitrogenous base.

FIG. 1 illustrates the reaction pathway for capturing CO₂ using solventmixtures comprising a nitrogenous base and a non-aqueous diluentaccording to the present invention. The reversible capture of CO₂according to this process involves a reaction with two equivalents of anitrogenous base diluted in a non-aqueous diluent. The reaction involvesformation of a carbamate and avoids the formation of a carbonate ester.As illustrated in FIG. 1, only the nitrogenous base (i.e., not thediluent) is shown to react with CO₂ from the gas stream, with capture ofCO₂ substantially (including solely) as a carbamate salt. The resultingsolution can be either ionic or non-ionic.

Accordingly, the invention provides a solvent system comprising asolution formed of: a nitrogenous base having a nitrogen with a hydrogenatom leaving group; and a diluent, wherein the nitrogenous base has astructure such that it reacts with an acidic gas so as to form acarbamate salt or a heteroatom analogue of a carbamate salt without anysubstantial formation of a carbonate ester, preferably with no formationof a carbonate ester. Substantial is defined herein as meaning that theproduct of the reaction is at least about 80% carbamate salt, at leastabout 98% carbamate salt, at least about 99% carbamate salt, at leastabout 99.5% carbamate salt, at least about 99.9% carbamate salt and mostdesirably, 100% carbamate salt. Thus, the product of the reaction can becharacterized as having less than about 20% carbonate ester, less thanabout 2% carbonate ester, less than about 1% carbonate ester, less thanabout 0.5% carbonate ester, less than about 0.1% carbonate ester, andmost desirably, 0% carbonate ester.

In certain embodiments, the diluent is selected such that it has lowmiscibility with water. For example, in some embodiments, the diluenthas a solubility of less than or equal to about 10 g/100 mL in water at25° C. (i.e., 10 g of solvent per 100 mL of water). In otherembodiments, the diluent has a solubility in water of less than or equalto about 0.01 g/100 mL, less than or equal to about 0.1 g/100 mL, lessthan or equal to about 0.5 g/100 mL, less than or equal to about 1 g/100mL, less than or equal to about 1.5 g/100 mL, less than or equal toabout 2 g/100 mL, less than or equal to about 2.5 g/100 mL, less than orequal to about 3 g/100 mL, less than or equal to about 4 g/100 mL, lessthan or equal to about 5 g/100 mL, less than or equal to about 6 g/100mL, less than or equal to about 7 g/100 mL, less than or equal to about8 g/100 mL, or less than or equal to about 9 g/100 mL in water at 25° C.In some embodiments, the diluent is completely immiscible with water.Using diluents with low water solubility may result in solvent systemsthat display one or more of the following attributes: they may requireless energy for regeneration; may have high CO₂ loading capacities; maybe able to tolerate water in the gas stream; and/or may be able to beseparated from water without a large energy penalty.

In additional embodiments, the nitrogenous based component of thesolvent system is similarly selected such that it has low miscibilitywith water. In preferred embodiments, the nitrogenous base has highermiscibility with the diluent than with water. In some embodiments, thenitrogenous base has high solubility in the diluent. Examples of suchnitrogenous bases include, but are not limited to, aliphatic amines withone or more hydrocarbon chains composed of three or more carbons, andaliphatic amines with one or more hydrocarbon chains composed of threeor more carbons with one or more fluorine atoms substituted for hydrogenin the hydrocarbon chain. It is noted that although diluents and/ornitrogenous bases having low miscibility with water are preferred, thepresent invention also encompasses solvent systems wherein the diluents,nitrogenous base, and/or combination thereof are at least partiallymiscible with water.

In some embodiments, the solvent system is tolerant to the presence ofwater. In certain embodiments, the solvent system tolerates water up toor equal to about 30% water by volume. For example, in some embodiments,the solvent system tolerates up to or equal to about 25% water byvolume, up to or equal to about 20%, up to or equal to about 15%, up toor equal to about 10%, up to or equal to about 5%, up to or equal toabout 2%, or up to or equal to about 1% water by volume. In someembodiments, tolerance to the presence of water means that there islittle to no degradation of the solvent performance up to the indicatedvolume of water. In some embodiments, the solvent system maintains at ornear its initial capacity for CO₂ loading up to the indicated volume ofwater.

In preferred embodiments, the CO₂ captured using the solvent system ofthe present invention may be released to regenerate the solvent systemfor reuse. It is preferred that the solvent system is regenerable (orreaction with the CO₂ is reversible) under mild conditions (e.g., at alow temperature). In some embodiments, the release of CO₂ andcorresponding regeneration of the solvent system is effectuated byheating the solution. When the solution containing bound CO₂ is heated,the chemical reaction is reversed and the CO₂ is released, producing aconcentrated CO₂ stream.

In some embodiments, the present application relates to a solvent systemand process for the removal of CO₂ from a gas stream. The presentinvention applies to any gas stream containing CO₂. For example, inparticular embodiments, the invention relates to a process for theremoval of CO₂ from fossil fuel combustion flue gas, a natural gasmixture, or a mixture of respiration gases from closed environmentscontaining CO₂. The process involves passing the mixed gas streamthrough a solvent system comprising a diluent and a nitrogenous basecomponent. In some embodiments, the present invention further relates tothe regeneration of the solvent system, which releases the CO₂. In someembodiments, regeneration of the solvent system involves heating thesolvent system at a temperature sufficient to release the CO₂. In someembodiments, the process involves heating the solvent system at atemperature at or below about 200° C., for example, at or below about185° C., at or below about 150° C., or at or below about 125° C. Inpreferred embodiments, the process involves heating the solvent systemat a temperature at or below about 100° C., for example, at atemperature at or below about 95° C., at or below about 90° C., at orbelow about 85° C., at or below about 80° C., at or below about 75° C.,or at or below about 70° C. In some embodiments, the CO₂ may be releasedat ambient temperature. In certain embodiments, the CO₂ is captured in anon-aqueous phase under conditions in which water accumulates as aseparate, lower density phase. This phase can be sent to the regeneratorwith the rich, non-aqueous phase to be regenerated at a lowertemperature than the corresponding rich aqueous phase alone. This can befollowed by phase separation from the lean, regenerated solvent beforebeing sent back to the absorber.

In certain embodiments, at or about 100% of the CO₂ is removed from theCO₂-rich solvent system. However, in other embodiments, less than 100%of the CO₂ is removed from the CO₂-rich solvent system. In preferredembodiments, about 50 to 100% of the captured CO₂ is removed from theCO₂-rich solvent system, preferably about 75% to 100%, about 80% to100%, about 90% to 100%, about 95% to about 100%, or about 98% to 100%.For example, in some embodiments, at least about 98%, 95%, 90%, 85%,80%, 75%, 70%, 60%, or 50% of the captured CO₂ is removed from theCO₂-rich solvent system.

In some embodiments, the removal of CO₂ from gas mixtures containing H₂Oin addition to CO₂ can lead to the accumulation of H₂O in the solventsystem, either as a single phase or biphase solution, depending upon thereaction conditions. As noted above, the presence of H₂O in the solventmixture may be disadvantageous because of an undesirable side reaction,and more energy will be required for solvent regeneration due to thenecessity of removing water from the solvent. Thus, the accumulation ofH₂O in the solvent system may increase the regeneration energy demand,decreasing the efficiency of the regeneration system.

In some embodiments, the process of the present invention provides amethod by which the detrimental effects of H₂O accumulation in thesolvent system may be avoided. For example, the detrimental effect ofH₂O accumulation on the solvent system regeneration energy demand may beminimized, by providing a process by which the CO₂ is captured withinthe solvent system at a temperature greater than the H₂O saturationtemperature of the gas mixture. Additionally, the detrimental effect ofH₂O accumulation on the solvent system regeneration energy demand may beminimized by providing a process by which the H₂O accumulates as aseparate, aqueous phase within the solvent system. This process involvesthe use of a solvent system that exhibits little or no solubility inwater. In such a system, water that collects is present as a separatephase. The separate, aqueous phase may be decanted or centrifuged off bymechanical, rather than thermal, processes, minimizing the energyrequired to maintain an efficient CO₂ removal system. For example, asthe hydrocarbon chain of aliphatic alcohols is increased in length, thesolubility of the alcohol in water decreases. This is also true forfluorinated alcohols. For example, 2,2,3,3,4,4,5,5-octafluoropentanol(“OFP”) is essentially immiscible with water. Thus, a solvent systemcomprising an appropriate nitrogen base and OFP forms a biphasic liquidsolution when combined with water. In such a solvent, water can beseparated from the solvent system without distillation or the use of amembrane by decanting or centrifugation of the aqueous layer from thefluorinated phase. In some embodiments, after removal of the H₂O, theCO₂-rich solvent system can be regenerated at a low temperature with theaddition of low boiling diluents to satisfy the partial pressurerequirements. The solvent system could thus avoid the added energypenalty associated with the distillation of water. By providing anon-aqueous CO₂ absorbing solvent system with low water solubility, thesolvent system has lower energy demands and milder regenerationconditions than those of aqueous or high-water affinity CO₂ solventsystems.

In some embodiments, a system for the removal of CO₂ from a gas streamis provided. A schematic of an exemplary system of the present inventionis depicted in FIGS. 2 through 6. The CO₂ removal system 10 includes anabsorber 12 configured with an inlet to receive a gas stream. The gasstream may come directly from, e.g., a combustion chamber of a boilersystem in a power generation plant. The gas stream may or may not bepassed through other cleaning systems prior to entering the CO₂ removalsystem. The absorber may be any chamber wherein a solvent system for theremoval of CO₂ is contained, having an inlet and outlet for a gasstream, and wherein the gas stream may be brought into contact with thesolvent system. Within the absorber, the CO₂ may be transferred fromgaseous phase to liquid phase according to the principles discussedherein. The absorber may be of any type; for example, the absorber maycomprise a spray-tower absorber, packed-bed absorber (includingcountercurrent-flow tower or cross-flow tower), tray-tower absorber(having various tray types, including bubble-cap trays, sieve trays,impingement trays, and/or float valve trays), venture absorber, orejector absorber. The temperature and pressure within the absorber maybe controlled. For example, in one embodiment, the temperature of theabsorber may be maintained at or near 50-60° C. and the absorber may bemaintained at or near atmospheric pressure. Thus, the absorber may beequipped with a heating/cooling system and/or pressure/vacuum system.

Within the absorber, the gas stream is brought into fluid contact withand passed through a solvent system comprising a diluent and anitrogenous base component. The solvent system reacts with the CO₂present in the gas stream, capturing it from the remaining components ofthe gas, and the resulting CO₂-free gas stream is released from theabsorber through an outlet. The solvent system continues to react withentering CO₂ as the mixed gas stream is passed through, until it becomes“rich” with CO₂. The absorber is optionally connected to one or morecomponents. For example, the absorber is preferably configured with ameans for routing solvent to a unit wherein water may be decanted,centrifuged, or otherwise removed from the system.

At any stage in the process of CO₂ capture, the solvent system may beregenerated. The system therefore includes an optional regenerationsystem 14 to release the captured CO₂ via a separate CO₂ gas stream andthus regenerate the solvent system. The regeneration system isconfigured to receive a feed of “rich” solvent from absorber and toreturn regenerated solvent to the absorber once CO₂ has been separatedfrom the “rich” solvent. The regeneration system may simply comprise achamber with a heating unit to heat the solvent system at a temperaturesufficient to release the gas, along with a release valve to allow theCO₂ to be removed from the regeneration system. It may also be adistillation column and have essentially the same design as describedabove for the absorption column. The regenerator may be optionallyconnected to one or more components. For example, the regenerator ispreferably configured with a means for routing solvent to a unit whereinwater may be decanted, centrifuged, or otherwise removed from thesystem.

The released CO₂ can be output to storage or for other predetermineduses. The regenerated solvent is again ready to absorb CO₂ from a gasstream, and may be directed back into the absorber.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

EXPERIMENTAL

The following example is provided for the purpose of complete disclosureand is not to be viewed as limiting of the invention.

Example 1: Reaction between CO₂ and 2-fluorophenethylamine in Solutionwith 4-methoxy phenol as Diluent

Reaction between CO₂ and 2-fluorophenethylamine (2-FPEA) in solutionwith a methyl substituted phenol, specifically for this example4-methoxy phenol (4-MeOPh), was initially observed using a standardsemi-batch reactor system in which the amine solution was contained inthe reaction vessel and a gas stream containing CO₂ was bubbled throughthe amine solution. The CO₂ concentration of the feed gas and reactoroutlet gas streams was monitored via a NDIR CO₂ analyzer to determineextent of CO₂-amine reaction. Upon introduction of the CO₂ containinggas stream to the amine solution resulted in a reduction in the CO₂content of the reactor outlet gas stream indicating that CO₂ wasreacting with the amine solution. Reaction with CO₂ was accompanied by asmall temperature rise in amine solution temperature from 25.5 to 27° C.due to the exothermic nature of the reaction. The reaction was continueduntil the CO₂ concentration in the reactor outlet stream achieved >95%of the feed concentration. Integration of the quantity of CO₂ reactedwith the amine solution indicated that a CO₂:amine molar ratio of 0.37:1was achieved.

Reversibility of the reaction between CO₂ and the 2-FPEA/4-MeOPh solventsystem was observed by ramping the temperature of the 2-FPEA/4-MeOPh/CO₂system, described above, to 80° C. under a N₂ purge. The release of CO₂from the CO₂-containing solution was monitored via a NDIR CO₂ analyzer.Integration of the quantity of CO₂ released indicated that CO₂ wascompletely released from both solvent systems.

Example 2: Reaction between CO₂ and 2-fluorophenethylamine in Solutionwith 2,2,3,3-tetrafluoropropanol (TFP) and2,2,3,3,4,4,5,5-octafluoropentanol (OFP) as Diluents

Reaction between CO₂ and 2-fluorophenethylamine (2-FPEA) in solutionwith fluorinated alcohols, specifically for this example2,2,3,3-tetrafluoropropanol (TFP) and 2,2,3,3,4,4,5,5-octafluoropentanol(OFP), was initially observed using a standard semi-batch reactor systemin which the amine solution was contained in the reaction vessel and agas stream containing CO₂ was bubbled through the amine solution. TheCO₂ concentration of the feed gas and reactor outlet gas streams wasmonitored via a NDIR CO₂ analyzer to determine extent of CO₂-aminereaction. For both amine solutions, 2-FPEA/TFP and 2-FPEA/OFP, theuptake of CO₂ was very rapid and near complete removal of CO₂ from theflowing gas stream was observed. Reaction with CO₂ was accompanied by arise in amine solution temperature from 26.5 to 29.5° C. (2-FPEA/TFP)and 23.6 to 26.6° C. (2-FPEA/OFP) due to the exothermic nature of thereaction. The reaction was continued until the CO₂ concentration in thereactor outlet stream achieved >95% of the feed concentration.Integration of the quantity of CO₂ reacted with the amine solutionindicated that a CO₂:amine molar ratio of 0.43:1 for the 2-FPEA/TFP and0.47:1 for 2-FPEA/OFP was achieved.

¹⁹F NMR was performed for the 2-FPEA/OFP/CO₂ mixture to characterize theproduct of the amine-CO₂ reactions. Deuterated chloroform was used asthe NMR solvent. ¹⁹F NMR of the 2-FPEA/OFP mixture is shown in the topspectrum of FIG. 7. Five unique ¹⁹F resonances correspond to thefluorine nuclei labeled F1 associated with 2-FPEA and F2, F3, F4, and F5associated with OFP are observable. After purging the 2-FPEA/OFP mixturewith CO₂, a total of six unique ¹⁹F resonances are observed thatcorrespond to the fluorine nuclei labeled F1, F1′, F2, F3, F4, and F5 asshown in the bottom spectrum of FIG. 7. The new F1′ resonance isassociated with the CO₂-amine reaction product—2-fluorophenethylaminecarbamate. No shift in the fluorine nuclei associated with OFP wasobserved, indicating that the fluorinated alcohol was not involved inthe CO₂-amine reaction pathway and serves as a diluent.

Example 3: Reaction between CO₂ and 2-fluorophenethylamine in Solutionwith Chloroform as Diluent

Observation of the reaction between CO₂ and 2-fluorophenethylamine(2-FPEA) in solution with chlorinated hydrocarbons, specifically forthis example deuterated chloroform, was observed by ¹H and ¹⁹F NMR. AnNMR experiment was conducted in deuterated chloroform solvent containingonly 2-fluorophenethylamine. ¹⁹F NMR of 2-FPEA/deuterated chloroformmixture is shown in the top spectrum of FIG. 8 and shows a single ¹⁹Fresonance corresponding to the fluorine nuclei labeled F1 associatedwith 2-FPEA. After purging the 2-FPEA/deuterated chloroform mixture withCO₂, a total of two unique ¹⁹F resonances are observed that correspondto the fluorine nuclei labeled F1 and F1′ as shown in the bottomspectrum of FIG. 8. The new F1′ resonance is associated with theCO₂-amine reaction product—2-fluorophenethylamine carbamate. Thecorresponding ¹H NMR spectra, shown in FIG. 9 also indicate that the2-fluorophenethylamine carbamate is formed. Notably, the resonances forthe amide N—H (H8) and protonated —NH₃ ⁺(H1) are clearly observable. Noevidence for the involvement of the involvement of the chlorinatedhydrocarbon in the CO₂-amine reaction pathway was observed indicatingthat it acts as a diluent.

Example 4: Reaction between CO₂ and 3-fluoro-N-methylbenzylamine with2,2,3,3,4,4-hexafluorobutanol (HFB) and4,4,5,5,6,6,7,7,7-nonafluoroheptanol (NFHp) as Diluent

Reaction between CO₂ and 3-fluoro-N-methylbenzylamine (3-FNMBA) insolution with fluorinated alcohols, specifically for this example2,2,3,3,4,4-hexafluorobutanol (HFB) and4,4,5,5,6,6,7,7,7-nonafluoroheptanol (NFHp), was initially observedusing a standard semi-batch reactor system in which the amine solutionwas contained in the reaction vessel and a gas stream containing CO₂ wasbubbled through the amine solution. The CO₂ concentration of the feedgas and reactor outlet gas streams was monitored via a NDIR CO₂ analyzerto determine extent of CO₂-amine reaction. For both amine solutions,3-FNMBA/HFB and 3-FNMBA/NFHp, the uptake of CO₂ was very rapid and nearcomplete removal of CO₂ from the flowing gas stream was observed.Reaction with CO₂ was accompanied by a rise in amine solutiontemperature from 25.2 to 28.7° C. (3-FNMBA/HFB) and 21.9 to 26.4° C.(3-FNMBA/NFHp) due to the exothermic nature of the reaction. Thereaction was continued until the CO₂ concentration in the reactor outletstream achieved >95% of the feed concentration. Integration of thequantity of CO₂ reacted with the amine solution indicated that aCO₂:amine molar ratio of 0.36:1 for the 3-FNMBA/HFB and 0.47:1 for3-FNMBA/NFHp was achieved.

¹H and ¹⁹F NMR was performed on the 3-FNMBA/NFHp/CO₂ mixture tocharacterize the product of the amine-CO₂ reactions. Deuteratedchloroform was used as the NMR solvent. FIG. 10 shows the two reactionpathways with CO₂ which could be theorized for the solvent. All relevanthydrogen and fluorine nuclei are labeled. ¹⁹F NMR of the 3-FNMBA/NFHpmixture is shown in the top spectrum of FIG. 11. After purging the3-FNMBA/NFHp mixture with CO₂, a total of six unique ¹⁹F resonances areobserved that correspond to the four associated with the diluentfluorinated heptanol (F2, F3, F4, F5), one associated with the aminestarting material (F1), and one associated with the carbamate salt (F1′)as shown in the bottom spectrum of FIG. 11. The new F1′ resonance isassociated with the CO₂-amine reaction product—3-FNMBA carbamate.Examination of the ¹H NMR (FIG. 12) of the 3-FNMBA/NFHp mixture (top)compared to the ¹H NMR of the 3-FNMBA/NFHp/CO₂ mixture (bottom) alsoshows no change in the resonances associated with the methylene C—Hbonds of the fluorinated alcohol (H1, H2, H3). Instead, only ¹Hresonances associated with carbamate formation are observed (H6′, H7′,H8′). No shift in the proton or fluorine nuclei associated with NFHp wasobserved indicating that the fluorinated alcohol was not involved in theCO₂-amine reaction pathway and serves as a diluent.

Reversibility of the reaction between CO₂ and the 3-FNMBA/HFB and3-FNMBA/NFHp solvent systems was observed by ramping the temperature ofthe 3-FNMBA/HFB/CO₂ and 3-FNMBA/NFHp/CO₂ systems, described above, to80° C. under a N₂ purge. The release of CO₂ from the CO₂-containingsolution was monitored via a NDIR CO₂ analyzer. Integration of thequantity of CO₂ released from the 3-FNMBA/HFB/CO₂ and 3-FNMBA/NFHp/CO₂systems indicated that CO₂ was completely released from both solventsystems.

Example 5: Reaction between CO₂ and 3-fluoro-N-methylbenzylamine inSolution with Chloroform as Diluent

Observation of the reaction between CO₂ and 3-fluoro-N-methylbenzylamine(3-FNMBA) in solution with chlorinated hydrocarbons, specifically forthis example deuterated chloroform, was observed by ¹H and ¹⁹F NMR. AnNMR experiment was conducted in deuterated chloroform solvent containingonly 3-FNMBA. ¹⁹F NMR of 3-FNMBA/deuterated chloroform mixture is shownin the top spectrum of FIG. 13 and shows a single ¹⁹F resonancecorresponding to the fluorine nuclei labeled F1 associated with 3-FNMBA.After purging the 3-FNMBA/deuterated chloroform mixture with CO₂, atotal of two unique ¹⁹F resonances are observed that correspond to thefluorine nuclei labeled F1 and F1′ as shown in the bottom spectrum ofFIG. 13. The new F1′ resonance is associated with the CO₂-amine reactionproduct—3-fluoro-N-methylbenzylamine carbamate. The corresponding ¹H NMRspectra, shown in FIG. 14 also indicate that the3-fluoro-N-methylbenzylamine carbamate is formed. Notably, theresonances for the amide N—H (H2) and protonated —NH₂ ⁺(H2′) are clearlyobservable. No evidence for the involvement of the involvement of thechlorinated hydrocarbon in the CO₂-amine reaction pathway was observedindicating that it acts as a diluent.

The invention claimed is:
 1. A process for the removal of acid gas froma gas stream, comprising contacting an acid gas-containing gas streamwith a solvent system comprising a solution formed of: a nitrogenousbase having a nitrogen with a hydrogen atom leaving group; and anon-aqueous diluent, wherein the nitrogenous base has a structure suchthat it reacts with an acidic gas so as to form a carbamate salt or aheteroatom analogue of a carbamate salt without any substantialformation of a carbonate ester or heteroatom analogue of a carbonateester, wherein the solvent system is substantially insoluble in water,and wherein the diluent is selected from the group consisting of2,2,3,3,4,4,5,5-octafluoropentanol (” OFP″); 2,2,3,3-tetrafluoropropanol (“TFP”); 2,2,3,3,3 -pentafluoropropanol (“PFP”);2,2,3,3,4,4-hexafluorobutanol (“HFB”); nonafluoro-1-hexanol;4,4,5,5,6,6,7,7,7-nonafluoroheptanol ;1,1,3,3-hexafluoro-2-phenyl-2-propanol; 4-methoxyphenol (“4-MeOPh”);4-ethoxyphenol (“4-EtOPh”); 2-ethoxyphenol; 4-propoxyphenol;benzimidazole; 1-trifluoroacetylimidazole; 2-trifluoromethylpyrazole;3,5 -bistrifluoromethylpyrazole; 3-trifluoromethylpyrazole; and mixturesthereof.
 2. The process of claim 1, further comprising outputting anacid gas-rich solvent and an acid gas-lean gas stream.
 3. The process ofclaim 1, further comprising regenerating the acid gas-rich solvent byapplying heat to form a regenerated solvent comprising a lower contentof acid gas than present in the acid gas-rich solvent.
 4. The process ofclaim 1, wherein the heat applied is derived from a source selected fromthe group consisting of low-pressure steam, hot flue gas, or acombination thereof.
 5. The process of claim 1, further comprisingregenerating the acid gas-rich solvent by applying heat sufficient torelease CO₂ from the carbamate salt or the heteroatom analogue of thecarbamate salt to form a regenerated solvent comprising a lower contentof acid gas than present in the acid gas-rich solvent.
 6. The process ofclaim 1, wherein the acid gas-containing gas stream is fossil fuelcombustion flue gas.
 7. The process of claim 1, wherein the contactingis conducted within an absorber selected from the group consisting of aspray-tower absorber, packed-bed absorber, tray-tower absorber, ventureabsorber, and ejector absorber.
 8. The process of claim 7, wherein theabsorber is configured to route the solvent system to a unit whereinwater can be decanted, centrifuged, or otherwise removed from thesolution.